The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Hydraulic pressure is used to activate some known torque-transfer clutches, including multi-plate friction clutches used on powertrain systems including hybrid powertrain systems. Known multi-plate friction clutches may have spin losses caused in part by fluid that resists rotation of clutch elements when a clutch is deactivated. Hydraulic pressure can be provided by a mechanically driven hydraulic pump that uses power originating from an engine.
Known powertrain systems include engine systems that stop operating during ongoing powertrain operation, including during a traffic stop, referred to as an autostop event. Subsequently, the engine can be restarted to provide tractive power, referred to as an autostart event. Known powertrain systems having engines configured to execute autostop and autostart events use electrically-powered auxiliary pump systems to supplement a mechanically driven hydraulic pump. Such electrically-powered auxiliary pump systems provide hydraulic pressure to activate and maintain activation of torque transfer clutches during autostop events when the mechanically driven hydraulic pump is not operating. An electrically-powered auxiliary pump system adds mass, increases complexity of hydraulic circuits and electrical circuits, consumes packaging space, and requires additional control circuitry.